made latest a special value in compare function

kirc-core/src/test/kotlin/de/cmdjulian/kirc/image/TagTest.kt

@@ -0,0 +1,38 @@
+package de.cmdjulian.kirc.image
+
+import io.kotest.matchers.comparables.shouldBeEqualComparingTo
+import io.kotest.matchers.comparables.shouldBeGreaterThan
+import io.kotest.matchers.comparables.shouldBeLessThan
+import org.junit.jupiter.api.Test
+
+class TagTest {
+    @Test
+    fun `should be equal for latest`() {
+        Tag.LATEST shouldBeEqualComparingTo Tag.LATEST
+    }
+
+    @Test
+    fun `should be equal`() {
+        Tag("1.2.0") shouldBeEqualComparingTo Tag("1.2.0")
+    }
+
+    @Test
+    fun `should be smaller`() {
+        Tag("1.2") shouldBeLessThan Tag("1.3")
+    }
+
+    @Test
+    fun `should be bigger`() {
+        Tag("1.3") shouldBeGreaterThan Tag("1.2")
+    }
+
+    @Test
+    fun `latest is always greater`() {
+        Tag.LATEST shouldBeGreaterThan Tag("99999999")
+    }
+
+    @Test
+    fun `nothing is greater than latest`() {
+        Tag("99999999") shouldBeLessThan Tag.LATEST
+    }
+}

kirc-image/src/main/kotlin/de/cmdjulian/kirc/image/Reference.kt

@@ -15,7 +15,12 @@ class Tag(@JsonValue private val value: String) : Reference, Comparable<Tag> {
     }
 
     override val separator: Char get() = Companion.separator
-    override fun compareTo(other: Tag): Int = value.compareTo(value)
+
+    override fun compareTo(other: Tag): Int = when {
+        this == LATEST -> if (other == LATEST) 0 else 1
+        other == LATEST -> -1
+        else -> this.value.compareTo(other.value)
+    }
 
     override fun equals(other: Any?): Boolean = other is Tag && other.value == value
     override fun hashCode(): Int = value.hashCode()